Method of sintering and impregnating porous metal briquettes



Mach 5, 1940. 1 KURTZ 2,192,792

METHOD OF SINTERING AND IMPREGNATING POROUS METAL BRIQUETTES Filed July 28, 1938 INVENTOR Lee L. Ida-r2 Patented Mar. 5, 1940 UNITED STATES PATENT OFFICE METHOD OF SINT'EBING AND MPREGNAT- ING POROUS METAL BBJQUETTES tion of Delaware Application July 28, 1938, Serial No. 221,683

12 Claims.

This invention relates to a method of sintering briquettes made from powdered metal, and more particularly to a method of sintering such briquettes in a bath of molten metal which impregnates the briquette during the sintering thereof.

One of the objects of the invention is to provide a method for simultaneously sintering and impregnating briquettes made from powdered metal, wherein the impregnated metal is not readily soluble in the metal of the briquette.

A further object of the invention is to provide a method whereby briquettes made from powdered iron may be sintered and simultaneously impregnated with lead.

A still further object of the invention is to provide a method whereby a briquette made from powdered metal may be bath sintered in a bath of molten metal, said molten metal impregnating the briquette during the sintering operation.

Another object of the invention is to provide a method whereby iron or steel briquettes may be sintered under conditions which prevent carburization or decarburizaiton of the iron or,

, steel, and simultaneously impregnated with a metal which is not readily alloyable with the metal of the briquette.

Further objects and advantages of the present invention may be apparent from the following description, references being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

Fig. 1 illustrates an unsintered metal briquette, in the form of a cylindrical bearing.

Fig. 2 shows the briquette submerged in a bath of molten metal.

Fig. 3 diagrammatically illustrates the sintered and impregnated briquette in position upon a rotating spindle, and

Fig. 4 is an enlarged photomicrographic illustration depicting a cross-section of the impregnated and sintered briquetted material, in which the dark areas indicate the impregnated metal.

It is very difiicult when sintering briquettes, made from powdered iron or steel, to prevent a variation in carbon content of the ferrous metal during the sintering operation. This may be explained by the fact that when sintering briquetted powdered metals it is necessary to utilize a neutral, or reducing atmosphere on the furnace, since any oxidizing gas that is present tends to film the surfaces of the metal particles with their oxide and thereby weaken the bond between the particles. Neutral atmospheres are expensive and do not reduce surface oxides which may be present on the metal particles. For this reason, the present day trend is toward the use of reducing atmospheres in sintering furnaces. One of such reducing atmospheres is formed by in- 5 complete combustion of natural gas, having substantially-all the water vapor removed therefrom. This incompletely burned natural gas contains carbon dioxide, carbon monoxide, hydrogen, the remaining water vapor and nitrogen. Such a reducing gas has a decarburizing efiect upon articles of iron containing carbon and therefore when sintering iron briquettes in this atmosphere it has been found to be very diflicult to control the carbon content thereof.

When manufacturing bearings and many other articles for frictional or anti-frictional use, or in fact for many other uses, the sintered iron briquette is impregnated with some substantially insoluble metal, such as lead, to fill the pores of the briquette, and thereby provide a good surface for rubbing contact. The present invention is directed to a method whereby this impregnation can be simultaneously effected with the sintering step and wherein the sintering step occurs with the briquette out of contact with decarburizing. elements.

My invention consists in forming a briquette 20, under high pressure, from powdered iron, such as, sponge iron powder, comminuted iron or steel powder, electrolytic iron powder, or in fact any type of iron powder which is available. The iron powder prior to briquetting may be mixed with graphite or other desirable materials. The briquette so formed is next submerged in a bath of molten lead 22 preferably maintained at a temperature in the neighborhood of 2000 F. This temperature is not critical and may vary several hundred degrees in either direction but care should be taken that the temperature of 40 the bath does not exceed the melting point of iron. The temperature of the bath governs the period of immersion necessary to completely sinter the briquette. In the preferred embodiment, a sintering period of 10 minutes to one half an hour has produced satisfactory results. During the sintering operation the molten lead runs, by the aid of capillarity, into the pores, or interstices of the briquette and substantially fills the same, as noted in Fig. 4. The impregnating 5 action may be improved by evacuating the briquette prior to submersion in the lead bath and then applying pressure above the lead bath to force the lead into the briquette.

It is apparent that during the sintering operin the tin does not take up any appreciable quanatlon the iron in the briquette has not been subjected to any carburizing or decarburizing action, and therefore the sintered briquette has the same carbon content as was present in the unsintered briquette. In this manner a predetermined carbon content may be easily. maintained.

The sintered and impregnated briquette is next removed from the molten lead ath and placed on a revolving spindle 24, or in a centrifuge and the excess lead, which adheres to the surface of the briquette inthe molten condition, can be removed. In place of centrifugal action any other well known expedients may be utilized such as air blasts etc.

When desired the sintered iron briquette can be quenched to harden the same. This operation me 31 be carried out after the excess lead has been removed if the briquette is at a sufliciently high temperature or it may be carried out immediately after removal of the briquette from the lead bath. In the latter case the excess lead may be removed by passing the quenched briquette through a die to mechanically scrape the excess metal from the surface. thereof, or by machining.

While the foregoing description has been limited to the use of lead and iron for illustrative purposes only, it is apparent that other metals in the briquetted form can be sintered and impreghated in a molten metal in a similar manner. For example, briquettes of copper powder can be sintered and impregnated in lead baths, since lead and cor-per are not mutually soluble. Likewise, iron briquettes may be sintered and impregnated in molten bismuth as well as aluminum in either molten lead or cadmium. In each case care should be taken that the sintering bath is maintained below the melting point of the metal in the briquette.

The herein described method may also be carried out when using mixtures of metals in the unsintered briquette such as copper andtin powders used in the proportions of 90% Cu to 10% In this instance the lead although soluble tity thereof since the afllnity of tin for copper is so great than an equilibrium condition is quickly reached. Lead is not readily soluble in the resultant bronze and therefore remains dispersed therethrough in the impregnated substantially elemental state. Similar results are obtained when nickel is added to iron or when copper and nickel mixtures'are used in the briquette.

It is manifest that the sintering bath metal' must be onewhich is substantially insoluble in the predominating metal of the briquette, since if this is not the case, the predominanceof the molten metal will cause a dissolution of the briquette, destroying the metallic structure of the same and thereby lowering the strength and preventing the substantially uniform dispersion of the impregnated metal throughout the briquette, When desired, the briquette may be centrifuged :at an elevated temperature, or in a heated chamber, to cause the lead or other impregnated metal within the pores thereof-to be dispelled and thus leave the briquette porous. In this modification the surfaces of the porous metal remain wetted by the impregnating metal. It is manifest that the speed of centrifuging can be controlled to give any desired porosity or to only throw off the surface excess of impregnating metal as hereinbefore explained.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A method of sintering and simultaneously impregnating briquettes made from powdered metal, comprising the steps of; immersing a briquette of powdered metal in a bath of molten metal which is not readily soluble in the metal of the briquette, said bath being maintained above the melting point of the bath metal and at substantially the desired sintering temperature of the metal in the briquette, for such a time as to cause the metal of the briquette to sinter together and form a strong continuous metallic network having the metal of the bath substantially completely filling the pores thereof; and then removingthe sintered and impregnated briquette from the bath of molten metal.

2. A method of sintering briquettes made from powdered metal, comprising the steps of; forming a briquette from powdered metal by the application of high pressure; sintering said briquette in a molten bath of a metal which is not soluble in the metal of the briquette, at such a temperature and for such a time as to cause the particles in the briquette to fuse together to form a strong porous metal net-work with the metal of the bath completely filling said pores; and then removing the briquette from the bath and subjecting the same to a centrifugal operation while at an elethe external surface thereof.

3. A method of sintering and simultaneously impregnating briquettes of iron powder with lead and simultaneously preventing the briquette from changing in carbon content, comprising the steps of; forming a briquette from iron powder; immersing the briquette in a bath of molten lead maintained at a temperature well below the melting point of iron, for such a time as to cause the particles of iron to sinter together and form a strong metallic network having the lead completely filling the pores thereof and then removing the briquette from the lead bath and cooling the same.

4. A method of sintering and simultaneously impregnating briquettes of iron powder with lead and simultaneously preventing the briquette from changing in carbon content, comprising the steps of; forming a briquette from iron powder; immersing the briquette in a bath of molten lead maintained at a temperature well below the melting point of iron, for such a time as to cause the vated temperature, for removing excess metal on pletely filling the pores thereof; and then f quenching the sintered briquette to harden the lead while preventing the briquette from changing in carbon content, comprising the steps of; forming a briquette from iron powder; immersing the briquette in a bath of molten lead maintained at a temperature well below the melting point of iron, for such a time as to cause the particles of iron to sinter together and form a strong metallic network having the lead completely filling the pores thereof; and then centrifuging the briquette to remove the excess lead from the surface thereof.

6. In a method of heat treating briquettes made from powdered iron and simultaneously impregnating the briquettes so formed with lead, that step which comprises; sintering the iron briquette m a bath of molten lead maintained at a temperature below the melting point of iron.

'7. A method for impregnating articles made from briquetted iron powder with lead, comprising the steps of sintering the iron briquette in a bath of molten lead maintained at a temperature below the melting point of iron, for such a time to cause the particles of iron to fuse together and form a strong continuous network having the lead dispersed in, and completely filling, the pores thereof; and then removing the sintered briquette from the molten lead and removing the excess lead from the surface thereof.

8. A method of sintering and simultaneously impregnating briquettes made from powdered metal, comprising the steps of; immersing a briquette of powdered metal in a bath of molten metal which is not readily soluble in the metal of the briquette, said bath being maintained at a temperature below the melting point of the metal in the briquette, for such a time as to cause the metal of the briquette to sinter together and form a strong metallic network having the metal of the bath substantially completely filling the pores thereof; removing the sintered briquette from the molten metal; and then centrifuging the impregnated briquette for controlling the quantity of impregnated metal retained therein.

9; In a method of heat treating briquettes made from powdered iron, that step which comprises sintering the briquette by immersing the briquette in a bath of molten lead which is maintained at a temperature below the melting point of iron, and then removing the briquette from the bath.

10. In a method of sintering briquettes made from powdered iron and simultaneously coating the entire surface of the briquette with a soft metal which is insoluble in iron, that step comprising sintering the iron briquette by immersing the briquette in a bath of a molten metal which is substantially insoluble in iron, said bath being maintained above the melting point of the bath metal and at substantially the sintering temperature of the iron, removing the sintered and impregnated briquette from the bath, and then selectively removing the impregnated bath metal while the sintered briquette is maintained above the melting point of impregnating metal,

-whereby the porosity of the sintered briquette may be controlled.

11. In a method of heat treating briquettes made from powdered iron, and simultaneously coating the entire surface of the briquette with lead, the steps comprising, sintering the iron briquette by immersing the briquette in a bath of a molten lead said bath being maintained below the melting point of iron, removing the sintered briquette from the bath, and then selectively removing the impregnated lead, whereby the porosity of the sintered briquette may be controlled. 12. A method of sintering and simultaneously impregnating briquettes made from powdered iron comprising the steps of, immersing a briquette in a bath of molten metal which is not readily soluble in iron, said bath being'maintained at a temperature above the melting point of the bath metaland at substantially the sintering temperature of the iron, for such a time as to cause the iron powder .to sinter together and form a strong continuous network of iron having the metal of the bath substantially completely filling the pores thereof, and then removing the sintered and impregnated briquette from the molten metal. LEE L. KURTZ. 

